.img-wrapper{
    column-count: 4;
    column-gap: 10px;
    
    counter-reset: count;
    width: auto;
    margin: 0 auto;
    list-style: none;
}

.img-wrapper>li{
    position: relative;
    margin-bottom: 10px;
}
.img-wrapper>li>img{
    width: 100%;
    height: auto;
    vertical-align: middle;
}

.img-wrapper>li::after{
    counter-increment: count;
    content: counter(count);
    width: 2em;
    height: 2em;
    background-color: rgba(0,0,0,0.9);
    color: #ffffff;
    line-height: 2em;
    text-align: center;
    position: absolute;
    font-size: 1em;
    z-index: 2;
    left: 0;
    top: 0;
}